1. Field of the Invention
The present invention relates to a dental coating material, which is applied to surfaces of dental resin materials such as crown restoratives, dental fillers, and denture or denture base resins, and then polymerized upon irradiation with a visible light, thereby improving smoothness, durability and other properties of the surfaces of the dental resin materials.
2. Description of the Conventional Art
In the dental remedy in recent years, organic dental resin materials are widely employed for crown restoratives such as inlay, onlay, and crown, fillers for dental deficient portions, and denture base materials. For such dental resin materials, the surface of a material to be exposed within an oral cavity is desired to be smooth as far as possible. Accordingly, it is considered that careful polishing works are needed. As a result, in order to obtain a sufficient surface smoothness, there was involved a problem that a considerable period of time must be taken for polishing. Also, there was involved another problem that since the dental resin material is used under a severe condition within the oral cavity, coloration and staining occur due to the deterioration of the surface of the dental resin material. In order to solve these problems, there is employed a method in which after polishing the surface of the dental resin material into a smooth state, the surface of the dental resin material is coated with and protected by a dental coating material having a relatively high hardness, which is comprised of a polymerizable monomer as a major component.
Hitherto, ultraviolet light-polymerizable dental coating compositions comprising a photopolymerizable oligomer, a reactive monomer, and a ultraviolet light-sensitive polymerization initiator, while applying an acrylic hard coating technology widely used in the field of ultraviolet light-polymerization type inks, were used as the dental coating material. However, since a ultraviolet light having a biodetrimental effect was used during the polymerization of the ultraviolet light-polymerizable dental coating compositions, realization of dental coating materials, for which a safer visible light could be used, was demanded. Thus, various compositions containing a (meth)acrylate-based monomer and a photopolymerization initiator have been proposed as a visible light-polymerizable dental coating composition and are now used in various fields including one of a dental resin material.
However, when a photopolymerizable dental coating composition comprised of a (meth)acrylate-based monomer as a major component is irradiated with light, though a radical polymerization chain reaction is initiated to cause a polymerization reaction, since oxygen in air acts as a polymerization inhibitor at this time, an unpolymerized (meth)acrylate-based monomer remains on the surface of the polymerized and cured dental coating material. For this reason, the surface of the cured dental coating material fails in smoothness, even leading to a problem that it remains sticky for a long time without being cured. This problem was especially remarkable in the case of photopolymerization with a visible light rather than with a ultraviolet light.
In addition, Japanese Patent Laid-Open No. 183904/1988 proposes a dental coating material that is a visible light polymerization-curable composition comprised of a dipentaerythritol acrylate-based monomer, a volatile solvent for the monomer, and a polymerization initiator as major components and discloses camphor qunione as the photopolymerization initiator. However, since the camphor quinone as the photopolymerization initiator, which is widely used in the dental field, is colored yellow as a color by nature, compositions containing it are yellowish. Further, in cured films obtained upon irradiation with a visible light, a yellow color remains. Accordingly, there was a defect of being aesthetically inferior. In order to solve this defect, Japanese Patent Laid-Open No. 366113/1992 proposes a visible light polymerization-curable composition; and Japanese Patent Laid-Open No. 29910/1992 proposes a photopolymerizable dental surface coating material. However, there was still a problem that any of these materials is inferior in resistance to discoloration and stain resistance.
The invention is aimed to provide a photopolymerizable dental coating composition that, when applied to the surface of a dental resin material such as crown restoratives, dental fillers, and denture or denture base resins, is thoroughly cured upon irradiation with a visible light and produces a smooth, colorless and transparent cured surface after curing so that a film having superior durability, abrasion resistance and resistance to discoloration can be formed.
In order to achieve the above-described aim, we, the present inventors made extensive and intensive investigations. As a result, it has been found that the above-described aim can be achieved by a photopolymerizable dental coating composition in which a volatile (meth)acrylate compound and a polyfunctional acrylate as a cross-linking agent are used for rapidly performing the polymerization and imparting superior surface curing properties; a specific fluoroalkyl group-containing (meth)acrylate compound is used for improving durability, abrasion resistance and resistance to discoloration after curing; and a specific photopolymerization initiator having a high polymerization promoting effect for the foregoing monomers, which does not make the polymerized composition remain yellowish, is additionally used, leading to accomplishment of the present invention.
Specifically, the present invention is concerned with a photopolymerizable dental coating composition comprising (A) a polyfunctional acrylate, (B) a volatile (meth)acrylate compound, (C) a fluoroalkyl group constituted of at least one fluorocarbon-containing (meth)acrylate compound, and (D) an acyl phosphine oxide-based polymerization initiator. In particular, are preferred photopolymerizable dental coating compositions comprising (A) 10 to 70% by weight of a polyfunctional acrylate, (B) 10 to 70% by weight of a volatile (meth)acrylate compound, (C) 10 to 70% by weight of a fluoroalkyl group constituted of at least one fluorocarbon-containing (meth)acrylate compound, and (D) 0.1 to 10% by weight of an acyl phosphine oxide-based polymerization initiator. Of these are especially preferred those in which the fluoroalkyl group constituted of at least one fluorocarbon-containing (meth)acrylate compound as the component (C) is 2,2,2-trifluoroethyl methacrylate or 2,2,2-trifluoroethyl acrylate.